Structure for amorphous carbon based non-volatile memory

ABSTRACT

A memory device including at least one first memory element comprising a first layer of amorphous carbon over at least one second memory element comprising a second layer of amorphous carbon. The device also includes at least one first conductive layer common to the at least one first and the at least one second memory elements.

FIELD OF THE INVENTION

The invention relates to the field of random access memory (RAM) devicesformed using a resistance variable material.

BACKGROUND

Resistance variable memory elements, which include ProgrammableConductive Random Access Memory (PCRAM) elements, have been investigatedfor suitability as semi-volatile and non-volatile random access memoryelements. A typical PCRAM device is disclosed in U.S. Pat. No.6,348,365, which is assigned to Micron Technology, Inc.

A PCRAM device typically includes chalcogenide glass, for example, aGe_(x)Se_(100-x) glass, as the active switching material. A conductivematerial, such as silver, is incorporated into the chalcogenide glasscreating a conducting channel. During operation of the device, theconducting channel can receive and expel metal ions (e.g., silver ions)to program a particular resistance state (e.g., a higher or a lowerresistance state) for the memory element through subsequent programmingvoltages, such as write and erase voltages. After a programming voltageis removed, the programmed resistance states can remain intact for anindefinite period, generally ranging from hours to weeks. In this way,the typical chalcogenide glass-based PCRAM device functions as avariable resistance memory having at least two resistance states, whichdefine two respective logic states.

A chalcogenide glass-based device, however, can become unstable athigher temperatures. Accordingly, it is desired to have a memory devicebased on materials other than chalcogenide glass, particularly amaterial that would provide improved thermal stability. It is alsodesired to have a memory device with an architecture that permitsefficient surface area usage.

SUMMARY

Exemplary embodiments of the invention provide a memory device includingat least one first memory element comprising a first layer of amorphouscarbon over at least one second memory element comprising a second layerof amorphous carbon. The device also includes at least one firstconductive layer common to the at least one first and the at least onesecond memory elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages of the invention willbecome more apparent from the detailed description of exemplaryembodiments provided below with reference to the accompanying drawingsin which:

FIG. 1A illustrates a cross sectional view of a memory device accordingto an exemplary embodiment of the invention;

FIG. 1B illustrates an alternative exemplary embodiment of the memorydevice of FIG. 1A;

FIGS. 2A-2F illustrate cross-sectional views of the memory device ofFIGS. 1A and 1B at different stages of processing;

FIGS. 3A-3C illustrate the operation of the memory device of FIG. 1Aaccording to an exemplary embodiment of the invention;

FIG. 4 illustrates cross sectional view of a memory device according toanother exemplary embodiment of the invention;

FIG. 5 illustrates a cross sectional view of a memory device accordingto another exemplary embodiment of the invention;

FIG. 6A illustrates a three dimensional cross sectional view of a memorydevice according to another exemplary embodiment of the invention;

FIG. 6B illustrates a cross sectional view of the memory device of FIG.6A;

FIG. 7 illustrates a cross sectional view of a memory device accordingto another exemplary embodiment of the invention;

FIG. 8 illustrates a cross sectional view of a memory device accordingto another exemplary embodiment of the invention; and

FIG. 9 illustrates a processor system according to an exemplaryembodiment of the invention.

DETAILED DESCRIPTION

In the following detailed description, reference is made to variousspecific embodiments of the invention. These embodiments are describedwith sufficient detail to enable those skilled in the art to practicethe invention. It is to be understood that other embodiments may beemployed, and that various structural, logical and electrical changesmay be made without departing from the spirit or scope of the invention.

The term “substrate” used in the following description may include anysupporting structure including, but not limited to, a semiconductorsubstrate that has an exposed substrate surface. A semiconductorsubstrate should be understood to include silicon-on-insulator (SOI),silicon-on-sapphire (SOS), doped and undoped semiconductors, epitaxiallayers of silicon supported by a base semiconductor foundation, andother semiconductor structures. When reference is made to asemiconductor substrate or wafer in the following description, previousprocess steps may have been utilized to form regions or junctions in orover the base semiconductor or foundation. The substrate need not besemiconductor-based, but can be any support structure suitable forsupporting an integrated circuit. For example, the substrate can beceramic or polymer-based.

The term “silver” is intended to include not only elemental silver, butsilver with other trace metals or in various alloyed combinations withother metals as known in the semiconductor industry, as long as suchsilver alloy is conductive, and as long as the physical and electricalproperties of the silver remain unchanged.

The term “silver-selenide” is intended to include various species ofsilver-selenide, including some species which have a slight excess ordeficit of silver, for instance, Ag_(2+/−x)Se, where x is within therange of approximately 0 to approximately 1. Likewise, the term“tin-selenide” is intended to include various species of tin-selenide,including some species which have a slight excess or deficit of tin, forinstance, Sn_(1+/−x)Se, where x is within the range of approximately 0to approximately 1. Also, the term “antimony-selenide” is intended toinclude various species of antimony-selenide, including some specieswhich have a slight excess or deficit of antimony, for instance,Sb_(2+/−x)Se₃ or Sb_(2+/−x)Se₅, where x is within the range ofapproximately 0 to approximately 1.

The term “resistance variable memory element” is intended to include anymemory element that exhibits a programmable resistance change inresponse to an applied voltage.

Exemplary embodiments of the invention include a one time programmablememory device having one or more resistance variable memory elements,each including amorphous carbon as the active switching material (i.e.,the material that switches states corresponding to logical ones andzeros). It is known that amorphous carbon has a non-crystallinestructure including sp2 and sp3 hybridized carbon. The ratio of sp2 tosp3 hybridized carbon can vary. According to exemplary embodiments ofthe invention, the amount of sp3 hybridized carbon is greater than theamount of sp2 hybridized carbon. Unlike a typical chalcogenide-baseddevice, it has been experimentally shown that a memory element accordingto the invention is able to withstand very high temperatures (e.g.,greater than 260° C.) for periods of at least 30 minutes. Amorphouscarbon-based memory elements are described in more detail in U.S. PatentApplication No. [attorney docket no. M4065.1071/P1071], which isincorporated herein by reference and assigned to Micron Technology. Inc.

The memory devices according to the exemplary embodiments of theinvention have cross point-type architecture. Also, memory elements ofthe memory devices according to exemplary embodiments of the inventioncan be stacked to allow the device to have a greater number of memoryelements within the same surface area.

FIG. 1A depicts a first exemplary embodiment of a memory device 100constructed in accordance with the invention; and FIG. 1B depicts analternative exemplary embodiment of the memory device 100. The memorydevice 100 includes an array of stacked memory elements 101, 102. Thememory device 100 includes a first address line 41, which is coupled tofirst memory elements 101 through first plugs 30; and a second addressline 43, which is coupled to second memory elements 102 through secondplugs 31. The device 100 also includes first and second amorphous carbonlayers 20, 22. In the embodiment of FIG. 1A, silver lines 21 are locatedbetween the amorphous carbon layers 20, 22. Alternatively, as shown inFIG. 1B, a stack of layers 21-1, including conductive lines 21 b, can belocated between the amorphous carbon layers 20, 22.

The device 100 is supported by a substrate 10. Over the substrate 10,though not necessarily directly so, is the first conductive address line41. An insulating layer 11 can be provided between the substrate 10 andthe first address line 41. The first address line 41 serves as aninterconnect for a plurality of first memory elements 101. The firstaddress line 41 can be any material suitable for providing aninterconnect line, such as doped polysilicon, silver (Ag), gold (Au),copper (Cu), tungsten (W), nickel (Ni), aluminum (Al), platinum (Pt),titanium (Ti), among other materials.

The first address line 41 is connected to a plurality of firstconductive plugs 30. Each first conductive plug 30 serves as anelectrode for a respective memory element 101 and can be any suitableconductive material. For example, the first conductive plugs 30 can bedoped polysilicon, tungsten (W), nickel (Ni), aluminum (Al), platinum(Pt), titanium (Ti), among other materials. The conductive plugs 30 areformed within an insulating layer 15.

Over the first conductive plugs 30 is the first layer 20 of amorphouscarbon and the second layer 22 of amorphous carbon. The layers 20, 22are formed as blanket layers. In the exemplary embodiment of FIGS. 1Aand 1B, the first and second amorphous carbon layers 20, 22 have athickness within the range of approximately 50 Angstroms (Å) toapproximately 500 Å, and preferably between approximately 100 Å toapproximately 300 Å. The first and second amorphous carbon layers 20, 22have a greater amount of sp³ hybridized carbon than sp² hybridizedcarbon.

As shown in FIG. 1A, silver lines 21 are provided between the first andsecond amorphous carbon layer 20, 22. The silver lines 21 are formedperpendicular to the first and second address lines 41, 43. The silverlines 21 are formed within an insulating layer 121 and preferably have athickness within the range of approximately 300 Å to approximately 1000Å, and more preferably between approximately 300 Å to approximately 500Å. The silver lines 21 serve as an electrode for the memory elements101, 102.

Alternatively, as shown in FIG. 1B, each of the silver lines 21 caninstead be a stack of layers 21-1 including a conductive line 21 bbetween first and second metal containing layers 21 a, 21 c. Theconductive line 21 b serves as an electrode for its respective memoryelement 101, 102 and can be formed of any suitable conductive material.According to one exemplary embodiment, the conductive line 21 b istungsten. The metal containing layers 21 a, 21 c can be formed of, forexample, silver, tin-selenide (SnSe), antimony-selenide (SbSe), orsilver-selenide (AgSe). Also, in alternative embodiments, the first andsecond metal containing layers 21 a, 21 c can be blanket layers (notshown). In such a case, the first metal containing layer 21 a would be ablanket layer over the first amorphous carbon layer 20 and the secondmetal containing layer 21 c would be a blanket layer over the conductivelines 21 b and the insulating layer 121.

Second conductive plugs 31, which can be formed within an insulatinglayer 16, are provided over the second amorphous carbon layer 22.Similar to the first conductive plugs 30, the second conductive plugs 31can be any suitable conductive material, such as doped polysilicon,tungsten (W), nickel (Ni), aluminum (Al), platinum (Pt), titanium (Ti),among other materials. Each second conductive plug 31 serves as anelectrode to a respective memory element 102.

Each second conductive plug 31 is connected to the second address line43. Similar to the first address line 41, the second address line 43 canbe any material suitable for providing an interconnect line, such asdoped polysilicon, silver (Ag), gold (Au), copper (Cu), tungsten (W),nickel (Ni), aluminum (Al), platinum (Pt), titanium (Ti), among othermaterials. The address line 43 serves as an interconnect for a pluralityof memory elements 102.

The first conductive plugs 30 are located at points where the firstconductive line crosses below a silver line 21 (FIG. 1A) and the secondconductive plugs 31 are located at points where the second conductiveline crosses over a silver line 21. Alternatively, the first conductiveplugs 30 are located at points where the first conductive line crossesbelow a stack 21-1 (FIG. 1B) and the second conductive plugs 31 arelocated at points where the second conductive line crosses over a stack21-1. Accordingly, the locations at which the first conductive addressline 41 is coupled to the first amorphous carbon layer 20 through thefirst conductive plugs 30 define the memory elements 101.Correspondingly, the locations at which a second conductive address line43 is coupled to the second amorphous carbon layer 22 through the secondconductive plugs 31 define the memory elements 102. Therefore, eachsilver line 21 (or conductive line 21 b (FIG. 1B), serves as anelectrode to both memory elements 101 and memory elements 102. In thismanner, the memory elements 101, 102 are stacked allowing a greaternumber of memory elements 101, 102 to occupy a given amount of surfacearea than in a device having memory elements that are not stacked.

The first and second address lines 41, 43 and the silver lines 21 (orconductive lines 21 b) are each connected to operational circuitry 40,which is illustrated schematically in FIGS. 1A and 1B but which may beintegrated on a semiconductor substrate 10, and includes a voltagesource. Although only one first address line 41 and one second addressline 43 are shown, it should be appreciated that the device 100 caninclude a plurality of first and second address lines 41, 43. Duringoperation of the device 100, potentials are applied across one or moreof the memory elements 101, 102 to perform conditioning, write and/orread operations. The operation of the device 100 is described in moredetail below in connection with FIGS. 3A-3C.

FIGS. 2A-2F depict the formation of the memory element 100 according toan exemplary embodiment of the invention. No particular order isrequired for any of the actions described herein, except for thoselogically requiring the results of prior actions. Accordingly, while theactions below are described as being performed in a general order, theorder is exemplary only and can be altered if desired.

As shown in FIG. 2A, a substrate 10 is initially provided. As indicatedabove, the substrate 10 can be semiconductor-based or another materialuseful as a supporting structure. The insulating layer 11 is formed overthe substrate 10 and the first conductive address line 41 is formed overthe insulating layer 11. The insulating layer 11 can be formed of anysuitable material (e.g., silicon nitride, phosphosilicate glass,borosilicate glass, borophosphosilicate glass, among others) by knowntechniques. The first address line 41 is formed by depositing aconductive material, such as doped polysilicon, silver, gold, copper,tungsten, nickel, aluminum, platinum, titanium, among other materials.The conductive material is patterned to define the first address line41. The conductive material may be deposited by any technique known inthe art, such as sputtering, chemical vapor deposition, plasma enhancedchemical vapor deposition, evaporation, or plating, and subsequentlyetched, or a damascene and CMP process can be used.

An insulating layer 15 is formed over the first address line 41. Theinsulating layer 15 can be silicon nitride, a low dielectric constantmaterial, or other suitable insulators known in the art, and may beformed by any method. Preferably, the insulating layer 15 (e.g., siliconnitride) does not allow silver ion migration. Openings 215 are made inthe insulating layer 15 by, for instance, photolithographic and etchingtechniques.

As depicted in FIG. 2B, a layer of conductive material is deposited overthe insulating layer 15 and in the openings 215. The conductive materialis planarized, for example, by a chemical mechanical polish (CMP) step,to form first conductive plugs 30 within the openings 215. Any suitableconductive material, such as doped polysilicon, tungsten, nickel,aluminum, platinum, titanium, among other materials, can be used to formthe first conductive plugs 30.

The first amorphous carbon layer 20 is formed over the conductive plugs30 and insulating layer 15 by any suitable technique, as illustrated inFIG. 2C. According to exemplary embodiments of the invention, the firstamorphous carbon layer 20 is formed having a greater amount of sp3hybridized carbon than sp2 hybridized carbon. The first amorphous carbonlayer 20 is formed to a thickness within the range of approximately 50 Åto approximately 500 Å, and preferably between approximately 100 Å toapproximately 300 Å.

The insulating layer 121 is formed over the first amorphous carbon layer20. The insulating layer 121 can be formed of any suitable material byknown techniques, and is preferably formed of a material that does notpermit silver migration (e.g., silicon nitride). Preferably theinsulating layer 121 is formed having a thickness within the range ofapproximately 300 Å to approximately 1000 Å, and more preferably betweenapproximately 300 Å to approximately 500 Å. Openings 221 are then formedin the insulating layer 121, for example, by photolithographic andetching techniques. The openings 221 define the location of thesubsequently formed silver lines 21 (FIG. 2D). Therefore, the openings221 are formed as lines perpendicular to the first conductive addressline 41.

As depicted in FIG. 2D, a layer of silver is deposited over theinsulating layer 121 and in the openings 221. The silver layer isplanarized, for example, by a CMP step, to form silver lines 21 withinthe openings 221.

Alternatively, when a stack 21-1 (FIG. 1B) is to be formed instead ofsilver lines 21, a first metal containing layer 21 a, a conductive layer21 b, and a second metal containing layer 21 c are deposited over theinsulating layer 121 and within the openings 221. The layers 21 a, 21 b,21 c are then planarized to form stacks 21-1 within the openings 221.

A second amorphous carbon layer 22 is formed over the planarized silverlines 21 and insulating layer 121 by any suitable technique, asillustrated in FIG. 2E. Like the first amorphous carbon layer 20, thesecond amorphous carbon layer 22 is formed having a greater amount ofsp3 hybridized carbon than sp2 hybridized carbon. Preferably, the firstand second amorphous carbon layers 20, 22 have the same ratio of sp3hybridized carbon to sp2 hybridized carbon. The second amorphous carbonlayer 22 is formed to a thickness within the range of approximately 50 Åto approximately 500 Å, and preferably between approximately 100 Å toapproximately 300 Å.

An insulating layer 16 is formed over the second amorphous carbon layer22. The insulating layer 16 can be silicon nitride, a low dielectricconstant material, or other suitable insulators known in the art, andmay be formed by any method known in the art. Preferably, the insulatinglayer 16 (e.g., silicon nitride) does not allow silver ion migration.Openings 216 are made in the insulating layer 16 by, for instance,photolithographic and etching techniques.

As depicted in FIG. 2F, a layer of conductive material is deposited overthe insulating layer 16 and in the openings 216. The conductive materialis planarized, for example, by a CMP step, to form conductive plugs 31within the openings 216. Any suitable conductive material, such as dopedpolysilicon, tungsten, nickel, aluminum, platinum, titanium, among othermaterials, can be used to form the second conductive plugs 31.

The second conductive address line 43 (FIG. 1A) is formed over theconductive plugs 31 and insulating layer 16 by depositing a conductivematerial, such as doped polysilicon, aluminum, platinum, silver, gold,nickel, titanium, or tungsten. The conductive material maybe depositedby any technique known in the art, such as sputtering, chemical vapordeposition, plasma enhanced chemical vapor deposition, evaporation, orplating. The conductive material is then patterned to define the secondaddress line 43, such that the second address line 43 is parallel to thefirst address line 41 and perpendicular to the silver lines 21, toachieve the structure shown in FIG. 1A (or FIG. 1B). Alternatively, adamascene process can be used in which the conductive material isdeposited in trenches in an insulating layer and then CMP processed tothe surface of the insulating layer.

Additional processing steps can be conducted to complete the device 100.For example, interconnection lines, contacts, and circuitry are formedto connect the first and second address lines 41, 43 and the silverlines 21 (or conductive line 21 b (FIG. 1B)) to operational circuitry40.

FIGS. 3A-3C depict the operation of the memory device 100 (FIGS. 1A and1B) according to an exemplary embodiment of the invention. The operationof the device 100 is described with reference to a single memory element101 of FIG. 1A. It should be readily understood that the operation ofthe device 100 with respect to other memory elements 101, 102 isanalogous to that described with respect to the memory element 101 inconnection with FIGS. 3A-3C.

In the exemplary embodiment illustrated in FIG. 1A, once the memorydevice 100 is formed and prior to a conditioning step, the memoryelements 101 is in a high state of resistance. As shown in FIG. 3A, aconditioning operation is performed by applying a voltage pulse V₁ of agiven duration and magnitude using, for example, the voltage source ofoperational circuitry 40. It is believed that application of theconditioning voltage causes silver ions from the silver lines 21 to beincorporated into the first amorphous carbon layer 20 to form one ormore conducting channels 19 in the first amorphous carbon layer 20. Eachconducting channel 19 can support a conductive pathway 17 (FIG. 3B)during operation of the memory element 101. After application of theconditioning pulse, memory element 101 is in a medium state ofresistance.

In the medium resistance state, the memory element 101 is stillconsidered OFF (e.g., a first logic state). Once in a medium resistancestate, the element 101 remains OFF until a conducting channel 19receives excess silver ions from the silver lines 21 forming aconductive pathway 17 during a write operation.

Referring to FIG. 3B, during a write operation, excess silver ions fromthe silver lines 21 are believed to enter one or more of the conductingchannels 19 within the first amorphous carbon layer 20 forming a lowresistance conductive pathway 17. A write mode exists when a voltage V₂less than the conditioning voltage V₁ is applied across memory element101, thereby generating an ON state (low resistance state, e.g., asecond logic state) for memory element 101.

The device 100 of FIG. 1B including the stack of layers 21-1, instead ofsilver lines, can be operated in a similar manner. In the case of thedevice 100 of FIG. 1B, it is believed that metal ions from the metalcontaining layer 21 a, e.g., silver ions from a silver-selenide layer 21a, enter one or more of the conducting channels 19 within the firstamorphous carbon layer 20 forming a low resistance conductive pathway17.

During a write operation the silver ions migrate toward the negativepotential, here, the first address line 41, when applied across thememory element 101. The silver ions take the path of least resistanceinto the first amorphous carbon layer 20, which is provided by theconducting channels 19. The movement of the silver ions into aconducting channel 19 forms a low resistance conductive pathway 17.

A read operation is conducted by applying a read potential V₃, which isless than write potential V₂, to the memory element 101. In theexemplary embodiment depicted in FIG. 3C, the read potential V₃ isapplied to the memory element 101, which is in an OFF state (FIG. 3A).Current flow through the memory element 101 can be sensed by a currentsensing amplifier, which can be part of the operational circuitry 40 andprovides an output representing the resistance state of the memoryelement 101. The read voltage V₃ does not disturb other memory elements101, 102 (FIG. 1A) in the device 100, which are in the medium resistanceOFF state (FIG. 3A), since the read voltage V₃ is lower than the writevoltage V₂.

FIG. 4 depicts a memory device 400 according to another exemplaryembodiment of the invention. The memory device 400 is similar to thememory device 100 (FIGS. 1A and 1B), and includes an additional memorydevice stack 440 that includes memory elements 101′, 102′. For purposesof this specification a “′” following a reference numeral indicates anadditional structure of a like structure within a same device.Accordingly, for the device 400, the memory elements 101, 102 have asame structure as the additional memory elements 101′, 102′. As shown inFIG. 4, the second address line 43 also serves as a first address line41′ of the additional stack 440, such that there is a common addressline denoted as 43/41′.

While the memory device 400 is shown including silver lines 21, 21′, thedevice 400 could instead include stacks 21-1, 21-1′ like the memorydevice 100 (FIG. 1B). Although the memory device 400 is shown includingonly one additional memory device stack 440, the device 400 couldinclude a plurality of additional memory device stacks 440. The memorydevice 400 can be formed as described above in connection with FIGS.2A-2F, but with repeated processing steps to form the memory devicestack 440. Further, the memory device 400 can be operated as describedin connection with FIGS. 3A-3C.

FIG. 5 shows a memory element 500 according to another embodiment of theinvention. The memory device 500 is similar to the memory device 400(FIG. 4), except that the additional memory device stack 550 includes aseparate first address line 41′ instead of a common address line 43/41′(FIG. 4). An insulating layer 511 is formed between the second addressline 43 and the first address line 41′ of the additional stack 550.Although the memory device 500 is shown including only one additionalmemory device stack 550, the device 500 could include a plurality ofadditional memory device stacks 550. The memory device 500 can be formedas described above in connection with FIGS. 2A-2F, but with repeatedprocessing steps to form the memory device stack 550. Further, thememory device 500 can be operated as described in connection with FIGS.3A-3C.

FIGS. 6A and 6B illustrate a memory device 600 according to anotherexemplary embodiment of the invention. The memory device 600 is similarto the memory device 100 of FIGS. 1A and 1B, except that instead ofhaving silver lines 21 between the first and second amorphous carbonlayers 20, 22, the memory device 600 includes a blanket silver layer 621between first and second amorphous carbon layers 20, 22. Since thesilver layer 621 is a blanket layer, the first and second address lines41, 43 need not be formed parallel to one another. Alternatively, as inthe case of the memory device 100, the silver layer 621 can instead be astack of layers 21-1 (FIG. 1B) including a conductive layer 21 b betweenfirst and second metal containing layers 21 a, 21 c.

Additionally, the address lines 41, 43 are switchably connected to aplurality of conductive plugs 30, 31, respectively, by a plurality ofrespective first and second switching circuits 50, 51. The switchingcircuits are schematically illustrated in FIGS. 6A and 6B, and can beintegrated on a semiconductor substrate 10. In the exemplary embodimentdepicted in FIG. 6B, each first and second switching circuit 50, 51 is atransistor, but any suitable circuit can be used. Specifically, as shownin FIG. 6B, each first conductive plug 30 is switchably connected to thefirst address line 41 by a respective first switching circuit 50. Eachsecond conductive plug 31 is switchably connected to the second addressline 43 by a respective second switching circuit 51. During operation ofthe memory device 600, the switching circuitry serves to connect theaddress lines 41, 43 to memory elements 101, 102 and to isolate memoryelements 101, 102 from the first and second address lines 41, 43.Thereby, a particular memory element 101, 102 can be individuallyoperated.

In the embodiment of FIGS. 6A and 6B, the locations at which the firstconductive address line 41 is switchably coupled to the first amorphouscarbon layer 20 through the first conductive plugs 30 define the memoryelements 101. Correspondingly, the location at which a second conductiveaddress line 43 is switchably coupled to the second amorphous carbonlayer through the second conductive plugs 31 define the memory elements102.

The memory device 600 can be formed as described above in connectionwith FIGS. 2A-2F; except that the step of forming and patterning theinsulating layer 121 can be omitted. Additionally, instead of formingthe first and second conductive plugs 30, 31 in direct contact with thefirst and second address lines 41, 43, respectively, first and secondswitching circuits 50, 51 are formed such that the first and secondaddress lines 41, 43 are switchably coupled to the first and secondconductive plugs 30, 31. The switching circuits 50, 51 can be formed byknown techniques and the switching circuits 50, 51 can be coupled torespective conductive plugs 30, 31 and address lines 41, 43 byinterconnection lines and contacts, as is known in the art. The device600 can be operated as described in connection with FIGS. 3A-3C.

FIG. 7 illustrates a memory element 700 according to another embodimentof the invention. In the illustrated embodiment, the second address line43 also serves as a first address line 41′ of the additional stack 770,such that there is a common address line 43/41′. Although the memorydevice 700 is shown including only one additional memory device stack770, the device 700 could include a plurality of additional memorydevice stacks 770. While the memory device 700 is shown including silverlayers 621, 621′, like the memory device 600 (FIGS. 6A and 6B), thedevice 700 could instead include layer stacks 21-1 (FIG. 1B).

The memory device 700 can be formed as described above in connectionwith FIG. 6, but with repeated processing steps to form the memorydevice stack 770. Further, the memory device 700 can be operated asdescribed in connection with FIGS. 3A-3C.

FIG. 8 shows a memory element 800 according to another exemplaryembodiment of the invention. The memory device 800 is similar to thememory device 700 (FIG. 7), except that the additional memory devicestack 880 includes a separate first address line 41′ instead of a sharedaddress line 43/41′ (FIG. 7). Although the memory device 800 is shownincluding only one additional memory device stack 880, the device 800could include a plurality of additional memory device stacks 880. Thememory device 800 can be formed as described above in connection withFIG. 6, but with repeated processing steps to form the memory devicestack 880. Further, the memory device 800 can be operated as describedin connection with FIGS. 3A-3C.

FIG. 9 illustrates a processor system 900 which includes a memory device100 (FIG. 1) according to the invention. Although the processor system900 is shown including the memory device 100, the processor system 900could instead include a memory device according to a differentembodiment of the invention, for example, any one of memory devices 400,500, 600, 700, or 800 could be used in the processor system 900. Theprocessor system 900, which can be, for example, a computer system,generally comprises a central processing unit (CPU) 944, such as amicroprocessor, a digital signal processor, or other programmabledigital logic devices, which communicates with an input/output (I/O)device 946 over a bus 952. The memory device 100 communicates with theCPU 944 over bus 952 typically through a memory controller.

In the case of a computer system, the processor system 900 may includeperipheral devices such as a floppy disk drive 954 and a compact disc(CD) ROM drive 956, which also communicate with CPU 944 over the bus952. The memory device 100 may be combined with the processor, forexample CPU 944, in a single integrated circuit, if desired.

The above description and drawings are only to be consideredillustrative of exemplary embodiments, which achieve the features andadvantages of the present invention. Modification and substitutions tospecific process conditions and structures can be made without departingfrom the spirit and scope of the present invention. Accordingly, theinvention is not to be considered as being limited by the foregoingdescription and drawings, but is only limited by the scope of theappended claims.

1-67. (canceled)
 68. A method of forming a memory device, the methodcomprising the acts of: forming at least one first memory element, theact of forming the at least one first memory element comprising forminga first layer of amorphous carbon and forming at least one firstconductive layer; forming at least one second memory element over the atleast one first memory element, the act of forming the at least onesecond memory element comprising forming a second layer of amorphouscarbon and forming the at least one first conductive layer.
 69. Themethod of claim 68, wherein the act of forming the at least one firstconductive layer comprises forming the at least one first conductivelayer between the first and second amorphous carbon layers.
 70. Themethod of claim 68, wherein the acts of forming the first and secondamorphous carbon layers comprise forming the first and second amorphouscarbon layers having a greater amount of sp³ hybridized carbon than sp²hybridized carbon.
 71. The method of claim 68, wherein the acts offorming the first and second amorphous carbon layers comprise formingthe first and second amorphous carbon layers having a thickness withinthe range of approximately 50 Å to approximately 500 Å.
 72. The methodof claim 71, wherein the acts of forming the first and second amorphouscarbon layers comprise forming the first and second amorphous carbonlayers having a thickness within the range of approximately 100 Å toapproximately 300 Å.
 73. The method of claim 68, wherein the act offorming the at least one conductive layer comprises forming the at leastone conductive layer having a thickness within the range ofapproximately 300 Å to approximately 1000 Å.
 74. The method of claim 73,wherein the act of forming the at least one conductive layer comprisesforming the at least one conductive layer having a thickness within therange of approximately 300 Å to approximately 500 Å.
 75. The method ofclaim 68, wherein the act of forming the at least one first conductivelayer comprises forming a plurality of conductive lines.
 76. The methodof claim 68, wherein the act of forming the at least one firstconductive layer comprises forming the at least one conductive layerbetween the first and second amorphous carbon layers, and furthercomprising: forming a first conductive line over a substrate; forming asecond conductive line; coupling the first conductive line to the firstlayer of amorphous carbon at one or more locations to define at least afirst memory element; and coupling the second conductive line to thesecond layer of amorphous carbon at one or more locations to define atleast a second memory element.
 77. The method of claim 76, wherein theact of forming the second conductive line comprises forming the secondconductive line parallel to the first conductive line.
 78. The method ofclaim 76, wherein the act of coupling the first conductive line to thefirst layer of amorphous carbon comprises coupling the first conductiveline to the first layer of amorphous carbon at a plurality of locationsdefining a plurality of first memory elements, and wherein the act ofcoupling the second conductive line to the second layer of amorphouscarbon comprises coupling the second conductive line to the second layerof amorphous carbon at a plurality of locations defining a plurality ofsecond memory elements.
 79. The method of claim 76, wherein the act offorming the at least one first conductive layer comprises forming a samesilver blanket layer.
 80. The method of claim 79, wherein the act ofcoupling the first conductive line to the first layer of amorphouscarbon comprises switchably coupling the first conductive line to thefirst amorphous carbon layer, and wherein the act of coupling the secondconductive line to the second layer of amorphous carbon comprisesswitchably coupling the second conductive line to the second amorphouscarbon layer.
 81. The method of claim 80, further comprising the acts offorming at least one first conductive plug and at least one secondconductive plug, wherein the act of switchably coupling the firstconductive line comprises switchably coupling the first conductive lineto the first amorphous carbon layer through at least one firstconductive plug, and wherein the act of switchably coupling the secondconductive line comprises switchably coupling the second conductive lineto the second amorphous carbon layer through at least one secondconductive plug.
 82. The method of claim 76, wherein the act of formingthe at least one first conductive layer comprises forming a plurality ofsilver lines.
 83. The method of claim 82, wherein the act of forming theplurality of silver lines comprises forming the plurality of silverlines perpendicular to the first and second conductive lines.
 84. Themethod of claim 83, further comprising the acts of forming a pluralityof first conductive plugs connecting the first conductive line to thefirst amorphous carbon layer and forming a plurality of secondconductive plugs connecting the second conductive line to the secondamorphous carbon layer.
 85. The method of claim 76, further comprisingforming at least one first metal containing layer between the first andsecond amorphous carbon layers.
 86. The method of claim 85, furthercomprising the acts of forming first and second metal containing layers,wherein the act of forming the at least one first conductive layercomprises forming the at least one conductive layer between the firstand second metal containing layers.
 87. The method of claim 86, whereinthe acts of forming the first and second metal containing layerscomprise forming the first and second metal containing layers comprisingone of silver, tin-selenide, antimony-selenide, and silver-selenide. 88.The method of claim 76, further comprising the acts of: forming a thirdamorphous carbon layer; forming at least one second metal containinglayer over the third amorphous carbon layer; forming at least one secondconductive layer over the third amorphous carbon layer; forming a fourthamorphous carbon layer over the at least one second metal containinglayer and the at least one second conductive layer; and forming a thirdconductive line.
 89. The method of claim 88, further comprising the actsof: coupling the second conductive line to the third layer of amorphouscarbon at one or more locations to define at least a third memoryelement; and coupling the third conductive line to the fourth layer ofamorphous carbon at one or more locations to define at least a fourthmemory element.
 90. The method of claim 88, further comprising the actsof: forming a fourth conductive line; coupling the third conductive lineto the third layer of amorphous carbon at one or more locations todefine at least a third memory element; and coupling the fourthconductive line to the fourth layer of amorphous carbon at one or morelocations to define at least a fourth memory element.
 91. A method offorming a memory device, the method comprising the acts of: forming afirst conductive line over a substrate; forming a plurality of firstconductive plugs over the first conductive line; forming a firstamorphous carbon layer over the plurality of first conductive plugs;forming a plurality of first silver lines over the first amorphouscarbon layer; forming a second amorphous carbon layer over the pluralityof silver lines; forming a plurality of second conductive plugs over thesecond amorphous carbon layer; and forming a second conductive line overthe plurality of second conductive plugs.
 92. The method of claim 91,wherein the acts of forming the first and second amorphous carbon layerscomprise forming the first and second amorphous carbon layers having agreater amount of sp³ hybridized carbon than sp² hybridized carbon. 93.The method of claim 91, wherein the act of forming the plurality offirst silver lines comprises forming the plurality of first silver linesperpendicular to the first and second conductive lines.
 94. The methodof claim 91, further comprising the acts of: forming a third conductiveline; forming a plurality of third conductive plugs over the thirdconductive line; forming a third amorphous carbon layer over theplurality of third conductive plugs; forming a plurality of secondsilver lines over the third amorphous carbon layer; forming a fourthamorphous carbon layer over the plurality of second silver lines;forming a plurality of fourth conductive plugs over the fourth amorphouscarbon layer; and forming a fourth conductive line over the plurality offourth conductive plugs.
 95. The method of claim 94, further comprisingthe act of forming an insulating layer between the second and thirdconductive lines.
 96. The method of claim 94, wherein the acts offorming the first, second, third and fourth amorphous carbon layerscomprises forming the first, second, third and fourth amorphous carbonlayers having a greater amount of Sp³ hybridized carbon than sp²hybridized carbon.
 97. The method of claim 91, further comprising theacts of: forming a plurality of third conductive plugs over the secondconductive line; forming a third amorphous carbon layer over theplurality of third conductive plugs; forming a plurality of secondsilver lines over the third amorphous carbon layer; forming a fourthamorphous carbon layer over the plurality of second silver lines;forming a plurality of fourth conductive plugs over the fourth amorphouscarbon layer; and forming a third conductive line over the plurality offourth conductive plugs.
 98. The method of claim 97, wherein the acts offorming the second conductive line, the plurality of second conductiveplugs and the plurality of third conductive plugs comprise forming thesecond conductive line connected to the plurality of second conductiveplugs and the plurality of third conductive plugs.
 99. The method ofclaim 97, wherein the acts of forming the first, second, third andfourth amorphous carbon layers comprises forming the first, second,third and fourth amorphous carbon layers having a greater amount of sp³hybridized carbon than sp² hybridized carbon.
 100. A method of forming amemory device, the method comprising the acts of: forming a firstconductive line over a substrate; forming a plurality of firstconductive plugs switchably connected to the first conductive line;forming a first amorphous carbon layer over the plurality of firstconductive plugs; forming a first silver layer over the first amorphouscarbon layer; forming a second amorphous carbon layer over the firstsilver layer; forming a plurality of second conductive plugs over thesecond amorphous carbon layer; and forming a second conductive lineswitchably connected to the plurality of second conductive plugs. 101.The method of claim 100, wherein the acts of forming the first andsecond amorphous carbon layers comprises forming the first and secondamorphous carbon layers having a greater amount of sp³ hybridized carbonthan sp² hybridized carbon.
 102. The method of claim 100, furthercomprising the acts of: forming a third conductive line; forming aplurality of third conductive plugs switchably connected to the thirdconductive line; forming a third amorphous carbon layer over theplurality of third conductive plugs; forming a second silver layer overthe third amorphous carbon layer; forming a fourth amorphous carbonlayer over the second silver layer; forming a plurality of fourthconductive plugs over the fourth amorphous carbon layer; and forming afourth conductive line switchably connected to the plurality of fourthconductive plugs.
 103. The method of claim 102, wherein the acts offorming the first, second, third and fourth amorphous carbon layerscomprises forming the first, second, third and fourth amorphous carbonlayers having a greater amount of sp³ hybridized carbon than sp²hybridized carbon.
 104. The method of claim 100, further comprising theacts of: forming a plurality of third conductive plugs switchablyconnected to the second conductive line; forming a third amorphouscarbon layer over the plurality of third conductive plugs; forming asecond silver layer over the third amorphous carbon layer; forming afourth amorphous carbon layer over the second silver layer; forming aplurality of fourth conductive plugs over the fourth amorphous carbonlayer; and forming a third conductive line switchably connected to theplurality of fourth conductive plugs.
 105. The method of claim 104,wherein the acts of forming the first, second, third and fourthamorphous carbon layers comprises forming the first, second, third andfourth amorphous carbon layers having a greater amount of sp³ hybridizedcarbon than sp² hybridized carbon.